Wooden garage ideas

I looking to put a wooden garage at attached to the side of my house in fact only one end will probably be wood as the other wall is the house.
Back end I plan to use some wood resting on a small wall that's currently there.

The floor is 9 inch ready mix already, roof will be box profile sheets maybe with insultation depending on cost.

The reason for wood is because that side I have a large retaining wall and I don't want to add extra stress to it.

I don't plan on using it for a car mostly, it will be for storage for my tools.

Has anyone done similar I'm looking for ideas. What materials to use.
Obviously I need it to be waterproof.

So it's a permitted development but needs building regs because of combustible material on boundary

I did consider this to and could quite easily do that, but I wonder who may spot it and make a fuss that's my only concern. Lots of curtain twitchers around me